An apparatus main assembly not provided with a mechanism for moving a main assembly side engaging portion provided in the main assembly of the electrophotographic image forming apparatus to transmit a rotational force to a rotatable member such as an electrophotographic photosensitive drum, in response to an opening and closing operation of a main assembly cover of the apparatus main assembly, in a rotational axis direction of the main assembly side engaging portion, is known.
In addition, a structure of a process cartridge demountable, from the apparatus main assembly, in a predetermined direction substantially perpendicular to a rotational axis of the rotatable member is known.
Further, a structure for engaging a coupling member provided on the process cartridge with the main assembly side engaging portion is known.
As to the coupling type as such a rotational force transmission means, a structure is known in which the coupling member provided on an electrophotographic photosensitive drum unit is made pivotable relative to the rotational axis of the electrophotographic photosensitive drum unit so that an engaging operation and a disengaging operation of the coupling member with the mounting and demounting operation of the process cartridge relative to the apparatus main assembly (Japanese Patent No. 4498407).